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How do I add a curve fitted plot to this code?

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johnmurdock
johnmurdock on 8 Apr 2019
Answered: Sambit Senapati on 17 Apr 2019
clc
clear
close all
xls=xlsread("Exam2_Data.xls");
t=xls(:,1);
y=xls(:,2);
SST=sum((y-mean(y)).^2);
for i=1:3
fprintf('For %d order fit\n\n',i);
disp('Polynomial coefficients are');
C=polyfit(t,y,i);
SSR=sum((y-polyval(C,t)).^2);
R2=1-SSR/SST;
fprintf('R^2 is %f\n\n',R2);
end
for i=2:length(t)-1
T=[t(i-1) t(i) t(i+1)];
Y=[y(i-1) y(i) y(i+1)];
if(t(i)<33.75&&t(i+1)>33.75)
C=polyfit(T,Y,2);
disp('Value at 33.75 is ');
polyval(C,33.75)
return
end
end

  2 Comments

Rik
Rik on 9 Apr 2019
Do you mean like in a live script? Also, are you sure about the return? Don't you mean break? Return causes the current running function to return to the caller, while break causes the current (inner) loop to exit.
johnmurdock
johnmurdock on 9 Apr 2019
I mean I want to add a block of code that plots a curve fitted line with an equation over the data I pulled from excel. I will try break instead of return as well.

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Answers (1)

Sambit Senapati
Sambit Senapati on 17 Apr 2019
you can use the polyval and plot functions in tandem to do the job here:
instead of calling polyval(C,33.75) at a single data point, do the following:
>> Y_new=polyval(C,T);
>> plot(T,Y_new)
You could do this for your original data set as well.

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